Sorry that nobody has answered you as I'd also like to know this but - it's my understanding that there are changes that would be nearly impossible to reverse without restoring a full backup. I usually backup before each major change, but did not before injecting the first shot.
I know many of the changes are in the init.d folder and could likely be deleted, but this is only part of the changes (from what little I understand)
I know that personally I've had good luck with the shots and I'm on 9.5 and things are working swimmingly for me.